Minor typo: "coxcomb graph" v/s "coxcomb chart"

The "bad" and "good" diffs in section 19.2 had different text; making them the same to avoid confusion about what the difference is.

README.md

@@ -2204,7 +2204,7 @@ Other Style Guides
          firstName: 'Florence',
     -    lastName: 'Nightingale'
     +    lastName: 'Nightingale',
-    +    inventorOf: ['coxcomb graph', 'modern nursing']
+    +    inventorOf: ['coxcomb chart', 'modern nursing']
     };
 
     // good - git diff with trailing comma